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Undertow MadeYouReset HTTP/2 DDoS Vulnerability

High severity GitHub Reviewed Published Sep 2, 2025 to the GitHub Advisory Database • Updated Nov 15, 2025

Package

maven io.undertow:undertow-core (Maven)

Affected versions

< 2.2.38.Final
>= 2.3.0.Alpha1, < 2.3.20.Final

Patched versions

2.2.38.Final
2.3.20.Final

Description

A flaw was found in Undertow where malformed client requests can trigger server-side stream resets without triggering abuse counters. This issue, referred to as the "MadeYouReset" attack, allows malicious clients to induce excessive server workload by repeatedly causing server-side stream aborts. While not a protocol bug, this highlights a common implementation weakness that can be exploited to cause a denial of service (DoS).

References

Published by the National Vulnerability Database Sep 2, 2025
Published to the GitHub Advisory Database Sep 2, 2025
Reviewed Sep 2, 2025
Last updated Nov 15, 2025

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(29th percentile)

Weaknesses

Improper Resource Shutdown or Release

The product does not release or incorrectly releases a resource before it is made available for re-use. Learn more on MITRE.

Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Learn more on MITRE.

CVE ID

CVE-2025-9784

GHSA ID

GHSA-95h4-w6j8-2rp8

Source code

Credits

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